You are right in that the IV is the ‘06 length action.
I = 223 length
III = 308 length
IV = 30-06 length
V = magnum length
SM = short magnums
* there were some oddballs aswell. Such as the ppcs which were built on the III action but with a spacer in the magazine, and the early short mags were built on the V action with again a spacer in the mag.
Last edited by bigJ; 01/21/24.